Classification of Minerals
• Nearly 4000 minerals have been
identified on Earth (most of which we
don’t really worry about).
• Rock-forming minerals
• Common minerals that make up most of
the rocks of Earth’s crust
• Only a few dozen members
• Composed mainly of the 8 elements that
make up 98% of the continental crust
Classification of Minerals
• Silicates
• Most important mineral group
– Comprise most of the rock-forming minerals
– Very abundant due to large amounts of
silicon and oxygen in Earth’s crust
Silicate Mineral
Examples
Mica
Feldspar
Olivine
Quartz
Pyroxene
Building block of all silicates
Silica Tetrahedron
Four oxygen ions
surrounding a
much smaller
silicon ion
Classification of Minerals
• Silicate structures
• tetrahedra are linked together to form
various structures including
– Single tetrahedra
– Single and double chain structures
– Sheet or layered structures
Classification of Minerals
• Common Silicate minerals
(Mg,Fe)2SiO4
• Olivine
– High temperature Fe-Mg silicate called ferromagnesian (typical mantle mineral - formed
100’s km in Earth
– Individual tetrahedra linked together by iron
and magnesium ions
– Forms small, rounded crystals with no
cleavage
First mineral to crystallize out of a
basaltic magma
Classification of Minerals
• Common Silicate minerals
• Pyroxene Group for example (Mg,Fe)SiO3
– Single chain structures involving iron and
magnesium, chains weakly paired
– Two distinctive cleavages at nearly 90 degrees
– Augite is the most common mineral in the
pyroxene group
Classification of Minerals
• Common Silicate minerals
• Amphibole Group Ca2(Fe,Mg)5Si8O22(OH)2
– Double chain structures involving a variety of
ions
– Two perfect cleavages exhibiting angles of 124
and 56 degrees
– Hornblende is the most common mineral in the
amphibole group
Distinguish Hornblende from
Pyroxene Group by cleavage
Pyroxene Crystal
Two Cleavage Faces
at about 90 degrees
Hornblende Crystal
56 and 124 degree
Cleavages
Classification of Minerals
• Common Silicate minerals
• Mica Group
– Sheet structures that result in one direction of
perfect cleavage
– Biotite is the common dark colored mica mineral
– Muscovite is the common light colored mica
mineral
Muscovite
KAl3Si3O10(OH)2
Classification of Minerals
• Common Silicate minerals
• Feldspar Group
– Most common mineral group
– 3-dimensional framework of tetrahedra
exhibit two directions of perfect cleavage at
90 degrees
– Orthoclase (potassium feldspar) and
Plagioclase (sodium and calcium feldspar) are
the two most common members
Potassium feldspar
Note Pearly Luster!
KAlSi3O8
Plagioclase feldspar (Ca,Na)AlSi O
3 8
Note the Twinning, seems to have ‘stripes’
Minerals in Granite Rock: What is the pink stuff?
Classification of Minerals
• Common Silicate minerals
• Clay minerals
– Clay is a general term used to describe a variety
of complex minerals
– Clay minerals all have a sheet or layered
structure
– Most originate as products of chemical
weathering
Classification of Minerals
• Important nonsilicate minerals
• Several major groups exist including
– Oxides
– Sulfides
– Sulfates
– Native Elements
– Carbonates
– Halides
– Phosphates
Nonsilicate Mineral
Examples
Spinel
(Oxide)
Halite
(Halide)
Gypsum
(Sulfate)
Galena
(Sulfide)
Pyrite
(Sulfide)
Calcite
(Carbonate)
Hematite
(Oxide)
Classification of Minerals
• Important non-silicate minerals
• Carbonates contain CO3= fizzing with acid
– Primary constituents in limestone and dolostone
– Calcite (calcium carbonate) and Dolomite
(calcium-magnesium carbonate) are the two most
important carbonate minerals
Calcite showing cleavage faces
Classification of Minerals
• Important nonsilicate minerals
• Many nonsilicate minerals have economic
value
• Examples
– Hematite (oxide mined for iron ore)
– Halite (halide mined for salt)
– Sphalerite (sulfide mined for zinc ore)
– Native Copper (native element mined for copper)
Hematite, an oxide, Fe2O3
An important Iron ore. Very high density
Galena, PbS, a Sulfide
• An important ore of Lead
Gypsum, a Sulfate
.
CaSO4 2H2O
• An important evaporite mineral,
used to make sheetrock =drywall
Native Minerals – Copper
A pure element
Get a good start on your
workbook!
Next assignment
• Mineral ID from my samples (1 day) – for
marks
• Mineral ID from provincial exam photos.